According to multiple customers of Demon Internet - now owned by Brit telecom Thus - the London-based ISP is blocking access to all sites stored in the archive. When they query the Wayback Machine, hoping to retrieve archived pages, customers are met with generic "not found" error pages. But judging from their urls, these pages are generated by a web filter based on the blacklist compiled by the Internet Watch Foundation, a government-backed organization charged with policing online pornography.

One Demon customer tells us he was unable to visit archived versions of websites run by the BBC, Parliament, the United Nations, the Internet Watch Foundation, Demon Internet, and Thus. In other words, this customer points out, Thus is blocking its own web history. "It is nuts," he says.

His experience is confirmed by other Demon customers posting to a Demon newsgroup here.

We have contacted both Thus and the Internet Watch Foundation, but they did not receive our messages until after UK business hours. When they respond, we will update this story.

It is unclear why Demon's IWF filter would block the entire archive. Presumably, the archive is housing images flagged by the IWF, and in an effort to censor these images, Demon has censored everything. But it appears the problem does not extend to all ISPs. One Demon customer says he has no problem accessing the Wayback Machine from his Vodafone mobile internet service.

Another user calls the archive blockage "yet more 'unintended collateral damage' from the IWF. Didn't they actually learn anything from their Wikipedia disaster just before Christmas?"

In early December, under IWF instructions, at least six UK ISPs censored the Wikipedia entry dedicated to Virgin Killer, a mid-1970s record album from German heavy metal band The Scorpions. The album's original cover depicts a naked prepubescent girl.

The IWF had received a complaint about the Virgin Killer image, and after deciding the image may violate the UK Protection of Children Act, the British net censor added Wikipedia to a blacklist designed to shield ISPs customers "from inadvertent exposure to a potentially illegal indecent image of a child".

To block the image, those six ISPs began routing all Wikipedia traffic through a small number of transparent proxy servers, and in a roundabout way this resulted in Wikipedia banning edits from large swathes of the UK.

Because ISPs were squeezing all Wikitraffic through proxies, most editors appeared to be coming from the same IP range. If Wikipedia admins banned one editor for "vandalizing" the site, they banned untold thousands more.

But days later, after complaints from across the web, the IWF removed Wikpedia from its blacklist. "The IWF board has today considered [its previous] findings and the contextual issues involved in this specific case, and – in the light of the length of time the image has existed and its wide availability – the decision has been taken to remove this web page from our list," the net censor said. ®

Update

The IWF has responded to say "We’re investigating the issue more fully at the moment and will discuss it with Thus to get a better understanding of what has happened."

The not-for-profit wants to make it clear that "we only add URLs to our list and blocking is implemented by our member companies to ensure only access to specific URLs is blocked."

Customers of ISPs Be Unlimited and Virgin have also noticed some Internet Archive blocking.

Update 2

The IWF has now said that it has indeed blacklisted images housed by the Internet Archive. But its guidelines say that blacklisted URLs "are precise web pages" chosen so that "the risk of over blocking or collateral damage is minimised." And the organization will not speak for ISPs that seems to be blocking the entire archive (in some cases).

Is the Wayback Machine blocked on your ISP? If so, we would love to know. You can post a comment to this story below or email us here.